Concentrated cannabis resin, as well as isolated essences of THC, CBD, terpenes and other cannabinoids, act as a valuable tool in the medical world, allowing manufacturers to formulate products with accurate dosages for patients, in conveniently edible forms. As medicinal cannabis gains acceptance for its effectiveness, the demand for spirits of many varieties will increase. But not all extraction processes are equal. In this ongoing column, we will explore in depth the different types of extracts, methodologies and science behind emerging and traditional extraction technologies.
Full Spectrum Extract vs. Distillate
In the world of medical cannabis, “full-spectrum extract” or FSE simply refers to concentrated cannabis resin. The extraction is done in order to keep intact all cannabinoids and terpenes found in the original resin. FSE can be made using exclusively a variety of cannabis or a mixture of varieties, just like coffee or wine. Several studies have recently revealed that full-spectrum extracts are more effective at relieving certain symptoms than treatments based on individual compounds (for example, only THC or CBD) [1] [2]. The testimonial of the patients also supports this phenomenon, which scientists believe is due both to the presence of more pharmaceutical chemicals and to the beneficial synergistic interaction of chemicals, which is called the Phenomenon of Combinatorial Effect or Synergy.
Usually, hemp resin contains about 113 different cannabinoids and hundreds of different terpenes. In order to produce an “isolated distillate” of a specific compound found in the resin, FSE is used as a starting material and is obtained through a small short-process distillation process or membrane extraction. A technique called Separator Centrifugal Chromatography can isolate some of the lesser known cannabinoids, found in very low concentrations, for scientific research. This month we are focusing on the methods of obtaining the FSE, using solvents. Any of the FSE extracts produced by these methods, as well as by Supercritical CO2 extraction, can be used as a starting material for the distillation of THC, CBD, CBG, d-limonene, α-pinene etc. A future version of “All about Extraction” will focus on the production of spirits from various “raw” extracts.
With Solvents or Without
Many solvents can be used to extract the medicinal compounds from hemp. Below, we will look at ethanol hydrocarbons and solvents and keep the rich topic of using Supercritical CO2 as a solvent, for its own in-depth examination in a future article. The chemical properties of a substance determine how efficiently it extracts the desired compounds, as well as the potentially undesirable ones. A solvent degrades the plant resin, which binds to cannabinoids and terpenes as well as other compounds contained in the resin, such as waxes, lipids and chlorophyll. A “polar” solvent, which has an uneven distribution of electrons, attracts compounds that are also polar, and a “non-polar” solvent, with a more symmetrical distribution of electrons, is more easily connected to molecules that are also non-polar. Cannabinoids and terpenes are large organic molecules, which have some polar groups, but also contain many symmetrical carbon-hydrogen bonds, which are non-polar. Nonpolar interactions tend to dominate based on the size of molecules.
Solvent-free extraction may use either techniques with dry extraction of sieves, presses, or water-based, including stirring in microwaves and ultrasounds. None of the targeted compounds in cannabis resin are dissolved in water, so it is not considered a solvent. Water is extremely polar and the pharmaceutical compounds in cannabis are, for the most part, non-polar, with only minimal polarity. In next month’s issue, we will discuss solvent-free extraction techniques, from traditional hand-made methods to the latest technologies.
Extraction with Hydrocarbons
A popular extraction method is the use of hydrocarbon solvent such as propane, butane or hexane or a combination of these. These compounds consist entirely of symmetrical carbon-hydrogen bonds, are highly non-polar and are easily associated with THC, CBD, terpenes and other cannabinoids. They are also bound to the acidic forms of cannabinoids, such as THCA or CBDA, which are present in a high concentration in newly harvested material, although not as effectively as ethanol. Hydrocarbons have very low boiling points and are usually in gaseous form at room temperature and atmospheric pressure, which means that they are extremely prone to combustion when exposed to heat. That is why one should always perform the extraction, using a closed-circuit system in a laboratory with an active gas conductor, without heat sources or sparks.
Liquid hydrocarbon, under pressure and cooling, is injected through the plant material by dissolving the resin. The solution is then filtered through a micro-screen, before passing through a steam-absorbing pump, which collects and condenses the hydrocarbon solvent, for reuse. The resulting oil is placed in an evaporation device for further solvent removal: vacuum oven or rotary evaporator or thin glass evaporator filter (FFE).
Winterization
Because lipids and waxes are also non-polar, they are also extracted from hydrocarbons, along with cannabinoids and terpenes, so the resulting concentrate is not a clear substance. It usually looks like and is referred to as “wax” (like “butter”). Chlorophyll is also gently extracted, because it has a non-polar hydrocarbon tail, possibly contributing to the coloration of the extract in a slightly green or dark color. To achieve a clean, light-colored concentrate, the extract is subjected to an additional process called “Winterization”. First, the wax or trunk is placed in an ethanol bath, suitable for food, at room temperature. As the alcohol bath cools between -50 and -80 ° C, candles, lipids and chlorophyll solidify in cold ethanol while THC, cannabinoids and terpenes remain in watery or fluid form. This process usually takes 24-48 hours. The solution is then placed inside a micro-filter, allowing only ethanol, THC, cannabinoids and terpenes to pass through, filtering the frozen solid compounds. The filtered solution is then placed in a rotary evaporator or FFE to remove the remaining ethanol solvent.
Cryogenic Ethanol Extraction (CEE)
Ethyl alcohol, or ethanol (C2O5OH), has historically been used as an effective solvent for the production of hemp tinctures and oils. The chemical structure of ethanol makes it a unique solvent, capable of binding to both polar and non-polar compounds, because it contains both a polar hydroxyl-group (OH) and a non-polar ethyl hydrocarbon group. Because it is a small molecule, the polar and non-polar abilities of the solvent, have similar properties. Scientific experimentation shows that ethanol and other alcohols extract THC, CBD, THCA, CBDA, terpenes and other cannabinoids and flavonoids more effectively than hydrocarbon solvents [3].
With a boiling point much higher than most short-chain hydrocarbons (78.37 C compared to butane at -1 C), the risk of volatile explosions using ethanol is very low. However, at room temperatures, candles, lipids, and especially chlorophyll and other plant pigments dissolve much more easily in ethanol, than in non-polar hydrocarbon solvents, attributing a dark or green color to the concentrate.
The newly developed Cryogenic Ethanol Extraction involves reducing the ethanol temperature to between -60 and -80 °C and then injecting the cold liquid onto the plant material. Ultra-cold ethanol still attracts cannabinoids, terpenes and other pharmaceutical compounds, however lipids, waxes and pigments, such as chlorophyll, solidify and are much more difficult to extract. Therefore, cryogenically treated ethanol extract does not require the second stage of “winteraization” to produce a pure, extract known as the shatter.
The most efficient CEE technology is a closed-circuit system, in which successive amounts of pressure ethanol explode on the plant material in a vacuum chamber. Explosions are repeated several times in the same material, resulting in an extraction efficiency (EE) of 96-98%, of the THC contained in the reserve material, by this method [4]. Although this is the highest THC extraction yield of all known methods, the system behaves so that the more the extraction yield increases, the more chlorophyll there is and therefore the medicinal purity of the product decreases. Scientists continue to work to improve this critical aspect of the process. Ethanol is recovered and purified from the concentrate, using a rotary evaporator or FFE.
Both hydrocarbons and ethanol can produce high-quality full-spectrum extracts, maintaining the approximate synthesis of cannabinoids and terpenes found in the original material. Each solvent has its advantages and disadvantages, as discussed. Advances in technology and innovation continue to lead extraction scientists to increase the purity and pharmaceutical accuracy of these valuable drugs.
by Sama’a Djomehri
References:
[1] Adv Pharmacol. 2017;80:67-134. doi: 10.1016/bs.apha.2017.03.004. Epub 2017 Jun 5.
Cannabis Pharmacology: The Usual Suspects and a Few Promising Leads.
[2] Oncotarget. 2014 Aug; 5(15): 5852–5872.
Published online 2014 Jul 17. doi: 10.18632/oncotarget.2233
Cannabinoids as therapeutic agents in cancer: current status and future implications
Bandana Chakravarti,#1 Janani Ravi,#2 and Ramesh K. Ganju2
[3], https://blog.restek.com/?p=3018, August 3rd, 2011, Medical Marijuana Solvent Extraction Efficiency – Potency Determinations with GC-FID, Cochran, Jack and Rigdon, Amanda
[4] Capna Fabrications; https://prezi.com/view/jKFt7QeuW2TGSIJQqG4U/
